Download Pain, Distress, Analgesia and Anesthesia

CHAPTER 10
PAIN, DISTRESS, ANALGESIA AND ANESTHESIA
I.
How and by Whom are Levels of Pain and Distress Assessed and Categorized
The levels of pain and distress are initially categorized by the investigators as they
complete the protocol form. The IACUC then determines how appropriate their
selections are during protocol review. Criteria for assessing pain in different species
differ since species vary in their response to pain. Some species-specific behavioral
manifestations of pain or distress used as indicators include vocalization, depression or
other behavioral changes, abnormal appearance or posture and immobility. In rodents,
the signs of pain following surgery are manifested as decreases in food and water
consumption and weight gain, usually within the first 12 hours following the procedure.
These effects are not normally observed unless they are specifically measured. Other
signs of pain include reluctance to move, or guarding the surgical site (e.g. hunched
posture, limping). It is essential that the personnel caring for and using animals be
familiar with species-specific behavioral, physiologic and biochemical indicators of wellbeing. In general, unless the contrary is known or established it should be assumed that
procedures that cause pain in humans also cause pain in animals.
II.
IACUC Guidelines for Avoiding Unnecessary Pain or Distress
The IACUC has established guidelines on humane endpoints to ensure that unnecessary
pain or distress does not occur. These endpoints are directly related to the procedure, i.e.,
the size of the tumor, the mobility of the animal, the appetite of the animal, the activity
levels and the weight of the animal.
III.
Training and Experience of Personnel Performing Anesthesia
Individuals performing anesthesia should be trained by the investigator and the
veterinarian. Investigators providing the training should have had several years of
previous experience working with animals. All individuals performing anesthesia are
required to review UWM’s training manual and review appropriate surgery and
anesthesia tapes.
IV.
General Considerations of Anesthesia
A. What is Anesthesia?
Anesthesia is a state of unconsciousness induced in an animal. The three
components are analgesia or pain relief, amnesia and immobilization. Drugs used to
achieve anesthesia usually have varying effects in each of these areas. Some drugs
may be used to achieve all three and some need to be combined with others to
achieve full anesthesia.
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B. Pre-anesthetic Considerations
1.
2.
3.
Animals should be allowed a week to acclimate to a new environment after
transportation prior to anesthesia if possible.
Assess the animal prior to anesthesia to form a baseline for comparison in the
postoperative period.
It is not necessary to withhold food and water from rodents since vomiting does
not occur in these species.
C. Monitoring Anesthesia
1. Response to Pain
a) Pedal withdrawal reflex (toe pinch): using fingernails pinch web of skin
between animal’s toes. If the limb is withdrawn, the muscles twitch or the
animal cries out the depth of anesthesia is insufficient.
b) Tail pinch in small rodents: use as a substitute for pedal reflex.
2. Alteration in Eye Reflexes
a) Palpebral reflexes: touching the eyelids causes blinking. The animal is
light if it is blinking. Difficult to assess in small rodents
b) Corneal reflex: touching the cornea of the eye with a tuft of cotton causes
a blink. The animal is too deep if it has lost this reflex.
3. Alterations in Respiratory functions
a) Rate, depth and pattern can be monitored by watching the chest wall.
4. Alterations in the Cardio-Vascular System
a) Rate, rhythm and quality of peripheral pulse.
b) Stethoscope for heart sounds and rate.
5. Alterations in Blood Pressure
a) Quality of pulse: use femoral artery.
b) Capillary refill time: blanch gums with digital pressure.
6. Alterations in Temperature
a) Rectal temperature with clinical thermometer.
7. Muscle tone
a) Decreases as depth of anesthesia decreases, unless using cataleptic drugs; Test
by pulling on the lower jaw or a limb. Rigid tone indicates inadequate depth
of anesthesia.
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D. Anesthetic Problems and Emergencies
1.
Respiratory System
Most anesthetics cause direct depression of the respiratory center in the brain
and reduce ventilation. When an animal is in lateral recumbancy the lung that
is down is being compressed by the rest of the body. In dorsal recumbany the
animal may have depression of the diaphragm by abdominal viscera. The
airway can be compromised by regurgitated food or tracheal or pharyngeal
secretions due to normal reflexes being lost during anesthesia.
a. Signs of impending failure
 Rate: in rodents a decrease to less than 40 % of pre-anesthetic rate
indicates impending failure. Increased rate may indicate lightening
of level. Blue mucous membranes indicate a lack of oxygen.
b. Correction:
 Extend head and neck; open mouth and pull tongue forward.
 Ventilate with 100% oxygen if possible or assist ventilation by
manual compression of thorax- thumb and forefinger in rodents.
c. Prevention
 Pre-medication with atropine or glycopyrrolate (anticholinergics)
may reduce respiratory tract secretions in some animals.
 Intubate the trachea when possible to prevent aspiration pneumonia
and allow you to assist respiration.
2.
Cardiovascular System
Many anesthetics have direct effect on the heart or vasculature, decreasing
cardiac output and blood pressure.
a. Signs of impending failure
 Decreased capillary refill time; blanching of mucous membranes;
limbs cool to touch.
b. Correction
 Ensure unobstructed airway
 Ventilate with 100 % oxygen or with a face mask or with
intermittent compression of chest (gentle and rapid compression
between thumb and forefinger for rodents)
 For complete arrest: In rodents- easier to compress all areas of
thorax simultaneously and combine cardiac massage and assisted
ventilation.
c. Prevention
 Place an intravenous catheter whenever possible to provide access
for fluids.
 Supplemental fluids, IV, IP or SC; Rate of 5-10 ml/kg/hour;
Monitor for over-hydration or under-hydration.
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3.
Thermoregulation
Anesthesia frequently causes hypothermia because of inhalation of cold
gasses, exposure of body cavities to room air and loss of normal
thermoregulatory mechanisms and behaviors.
a. Prevention
 Monitor body temperature.
 Prevent heat loss by insulating cold surfaces.
 Supplement heat with a thermal blanket.
V.
Analgesia
To comply with PHS policies on minimizing pain and distress in laboratory animals,
analgesics are required for all vertebrates, including rodents that are subjected to a painful
procedure. Analgesia should be provided to animals if they undergo a procedure that is
likely to cause pain or distress, unless specific exception is granted by the IACUC based
on scientific justification. A painful procedure is considered to be any procedure that, in
the absence of evidence to the contrary, would cause pain in a human. Pain in rodents is
usually manifested as decreased activity, grooming or food and water consumption,
guarding behavior (e.g. limping or a hunched posture) or increased aggression. The
analgesic should be selected based on the level of pain expected. Ophthalmic, orthopedic
and visceral procedures will result in higher levels of post-operative pain than will skin
incisions, catheterizations, blood collection or subcutaneous implants.
Analgesics should be administered pre and postoperatively. If administered preoperatively they can reduce the dosage of anesthetic needed by 10 –15%. It is not
appropriate to wait until the signs of pain or distress are demonstrated before
administering analgesics since monitoring for clinical signs of pain may be an unreliable
method in rodents post anesthetic administration due to normal changes produced by the
anesthetics themselves.
A. Recognition of pain
1. Activity: reduced level or unusual restlessness; altered gait; altered posture
2. Appearance: lack of grooming; unusual posture
3. Temperament: aggressive or apathetic
4. Vocalizations: pitch of cry abnormal
5. Feeding: food and water intake are reduced; weight loss
6. Alterations in physiological variables: change in pattern and rate of respiration;
cardiovascular system may be altered; severe pain may cause shock.
VI.
Anesthetic/Analgesic Agents
Federal Regulations require that guidelines and consultation be provided to research
personnel on the type and amount of anesthetics, analgesics and tranquilizers used for
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each species of animal. Anesthetic agents and doses can be found on UWM’s Animal
Care Program website.
A. Inhalational anesthetics
Isoflurane is the first choice of anesthetic used for animal restraint or surgical
procedures in laboratory animal species. Isoflurane is delivered via a nose cone and
inhaled in rodents or provided through an intra-tracheal tube in larger species. The
concentration of drug can be administered to effect by adjusting the percent of
displacement of oxygen with a precision vaporizer and compressed oxygen.
Anesthetic chambers can be used for high vapor pressure anesthetics, however there is
great risk of overdose.
Advantages: Rapid induction and recovery. A precision vaporizer provides the ability
to precisely titrate the level of anesthesia during a procedure. Liquid Isoflurane is not
a DEA controlled drug and is non-explosive and non-flammable.
Disadvantages: Upfront cost associated with a precision vaporizer; requires either
passive or active scavenging of waste and exhaled anesthetic gas; occupational health
exposure to anesthetic gas should be limited; prolonged analgesic effect is not
achieved after the animal is awake; depressed respiratory rate and decreased blood
pressure.
Additional notes: The duration of anesthesia can be easily adjusted for a variety of
procedures ranging from 30 seconds up to many hours. Concurrent use of analgesics
such as opioids or NSAIDs is encouraged as Isoflurane has no analgesic properties
once the animal is awake from the procedures.
B. Injectable Anesthetics
Injectables are given to effect. Doses should be used as guidelines. Effects may vary
among individuals. Drugs that have exceeded their expiration date may not be used
even for terminal procedures. These agents can be given by the intra-venous, intramuscular, intra-peritoneal or subcutaneous routes. The agents are in general
metabolized in the liver and excreted in the kidneys. Inhalation agents are therefore
safer to use in debilitated animals.
1. Dissociative Agents
a. Ketamine (Ketoset®) , Tiletamine
Ketamine is the most commonly used injectable anesthetic in a variety of
species. In most cases, Ketamine is used in combination with other injectable
agents such as agonists or benzodiazepines to reduce or eliminate many of the
less desirable side effects if used alone. In rodents, ketamine combined with
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Xylazine or Xylazine plus Acepromazine are the preferred anesthetics when
gas anesthesia cannot be used.
Advantages: ketamine has a wide margin of safety in most species; residual
analgesic effect following anesthetic recovery, most commonly used drug in
combination for injectable anesthesia in rodents. Disadvantages: ketamine
alone does not provide muscle relaxation and muscle spasms may be
observed; DEA license required for use as Ketamine is a Schedule 111
controlled substance; surgical anesthesia may be limited depending on the
species; prolonged recovery as compared to gas anesthetics. The degree of
analgesia produced is variable and severe respiratory depression is produced
in small rodents. IP and IM injections are painful as the drug is acidic.
Additional notes: Produces a state of cataleptic sedation with apparent lack
of awareness of surroundings. The corneal blink reflex is lost in some species
and eye ointment should be applied to prevent drying of the cornea.
Laryngeal and pharyngeal reflexes are maintained and salivary secretions are
increased. Induction time for IM injections is 3 to 5 minutes and peak effect
lasts about 20 minutes. IP induction times are longer and recovery may be
prolonged. IV induction is rapid and provides about 10 minutes of anesthesia.
Ketamine combinations:
Ketamine plus Xylazine: Both drugs can be mixed in a single syringe prior to
administration. This is the most common injectable anesthetic used in rodent
species.
Ketamine plus Xylazine plus Acepromazine: All three drugs can be mixed in
one syringe. In rodents, the addition of Acepromazine to the cocktail
increases the depth of anesthesia and prolongs the duration of anesthesia as
well as recovery time.
Ketamine plus Diazepam: Both drugs can be mixed in a single syringe prior to
administration. In rodents, this combination only provides light anesthesia so
it may only be appropriate for chemical restraint.
b. Alpha-2 Agonists: Medetomidine (Domitor®), Dexmedetomidine
(Dexdomitor®), Xylazine (Rompun®)
Alpha-2 agonists are used for their sedative and analgesic properties in a
variety of species. Used as the sole agent, they do not produce an adequate
level of anesthesia for even minor surgical procedures. However, in
combination with Ketamine, they become much more useful and effective as
anesthetics for surgical procedures.
Advantages: Produces analgesia of short duration; can be combined with
Ketamine to produce adequate surgical anesthesia in many species; effects can
be reversed with a subcutaneous alpha- 2 antagonist injection; not a DEA
controlled drug; not irritating when administered IM or IP.
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Disadvantages: Cardiovascular depression (decreased heart rate, cardiac
output, and hypotension; transient hyperglycemia following administration
which may have research significance
Additional notes: When re-dosing an injectable anesthetic combination of
Ketamine and an alpha-2 agonist, it is recommended to only re-dose Ketamine
as the duration of action of the alpha-2 agonist is much longer than the
duration of the effect of Ketamine.
c. Alpha-2 Antagonists: Atipamezole (Antisedan®), Yohimbine
Alpha-2 antagonists are used a reversal agents for alpha-2 agonists.
Administration at the end of a procedure where the anesthetic combination
included Xylazine or Medetomidine, an alpha-2 antagonist will aid in
reducing anesthesia time and prompting anesthetic recovery.
Advantages: Can reduce duration of sedation and anesthesia caused by alpha2 agonist.
Disadvantages: Reverses any analgesic benefit of alpha-2 agonist; can cause
muscle tremors, increased respiratory rate and hyperemic mucous membranes.
d.
Benzodiazepines: Diazepam (Valium®), Midazolam, Zolazepam:
This class of drug can provide marked sedation in a variety of species;
however, there is no analgesic effect. These drugs are primarily used as
sedative, pre-anesthetics and the induction of anesthesia but are never used
alone to provide or maintain anesthesia.
e. Barbiturates: Sodium Pentobarbital(Nembutal®), Methohexital,
Thiopental
Barbiturates are irritating to tissues because of their acidic properties. They
redistribute rapidly to all body tissues so obese animals may require more
drug to anesthetize. Metabolism is slow so recovery times are slow. They are
controlled substances and as such require appropriate licensing to obtain and
appropriate record keeping. Barbiturates function as GABAa agonist and are
considered to be good anesthetic agents but provide unreliable sedation at low
dosages and inadequate analgesic effect at any dose.
Advantages: Rapid anesthetic onset; provides a prolonged duration of
surgical anesthesia;
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Disadvantages: Prolonged recovery time, inadequate analgesic properties;
extremely expensive; narrow margin of safety; produces respiratory
depression higher dosages; DEA License required
f. Opioids: Buprenorphine (Buprenex®), Oxymorphone, Fentanyl,
Morphine, Butorphanol
Opioid drugs produce their effect by binding three different receptors as either
agonists, partial agonist or antagonists.
Advantages: Provide potent analgesia; concurrent administration can lower
the dose of inhalant or barbiturate general anesthetic for surgery; mechanism
mediated by receptor binding in the brain and spinal cord; reversible with
Naloxone.
Disadvantages: DEA Controlled drugs; relatively short duration or action;
repeated use may result in tolerance development.
g. Non-steriodal Anti-Inflammatory Drugs (NSAIDs): Carprofen
(Rimadyl®), Meloxicam (Metacam®) Flunixin meglumine (Banamine®),
Ketoprofen (Ketofen®), Ibuprofen (Advil®)
Members of this group represent 13 different classes of drugs which share
inhibitory activity of cyclooxygenase enzyme.
Advantages: New drugs (Carprofen®, Meloxicam®) include a long duration
of analgesic activity; not a DEA controlled substance; there are multi-route
administration methods for several NSAIDs; relative safety when
administered at prescribed dosages.
Disadvantages: Contraindicated for inflammation models, infectious disease,
or coagulation research due to anti-inflammatory properties; COX-1 side
effects such as gastrointestinal complications, prolonged coagulation times,
and changes in kidney function with non-COX-2 selective forms.
Additional Notes: Analgesic combinations that include NSAIDs plus opioids
would be considered an ideal combination for the control and prevention of
discomfort due to the demonstrated harmony and difference in mechanism of
action. Oral dosing of analgesics following anesthesia results in questionable
consumption of the drug due to decreased water consumption following
anesthesia, as demonstrated in rodents.
h. Local anesthetics: Lidocaine, Bupivacaine (Marcaine®), Rjpivacaine
(Naropin®), Proparacaine (Alcaine® Ophthalmic)
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Local anesthetics block nerve impulses by specifically binding the voltage –
gate sodium channel in the nerve cell membrane. Local anesthetic routes of
administration include topical to mucus membranes or injected directly into
tissues and around nerve bundles. Use as the primary analgesic is discouraged
due to the short duration of effect (hours).
Advantages: Pre-operative and intra-operative administration can provide a
good adjunct in pain relief to general anesthesia and systemic analgesics
administered after a procedure. Drugs of this class are not controlled
substances.
Disadvantages: Avoid administering by intramuscular and intravenous
injections as both routes reach systemic circulation very rapidly. Dilution of
stock concentration is encouraged to provide more accurate does
administration.
Additional notes: Lidocaine is a fast acting, short duration local anesthetics.
Bupivacaine is a slow onset, long acting local anesthetic.
VII.
Additional Anesthesia/Analgesia Information by Species
A. Rat Anesthesia and Analgesia
1. Normal Parameters
a. Lifespan: 2-3 years (maximum 4)
b. Average weight: 250-400 gm
c. Heart Rate: 250-500 beats per minute
d. Respiratory Rate: 65-110/minute
e. Temperature: 99.2 degrees F average
f. Blood volume 6-7 % of body weight
g. Ear pinch most sensitive to assessing depth of anesthesia
B. Mouse Anesthesia and Analgesia
1. Normal Parameters
a. Lifespan: 1-2 years (maximum 3)
b. Average weight: 30 gms
c. Respiratory Rate: 60-220/minute
d. Temperature: 98.8 degrees F average
e. Blood volume: 5.5% of body weight
f. Surgical anesthesia- loss of withdrawal, corneal and tail pinch reflex
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C. Amphibian Anesthesia and Analgesia
Amphibians in the early stages of their life cycle (e.g., tadpoles) are entirely aquatic and
have gills for respiration. Most amphibians lose their gills during metamorphosis and
develop lungs. Most importantly, amphibian skin acts as a semipermeable membrane that
allows for respiration (cutaneous respiration) and absorption of substances through the
skin.
Amphibians may be anesthetized by immersion in an anesthetic solution, placement in an
anesthetic gas induction chamber or by anesthetic preparations applied to the skin.
Amphibians can remain out of water for long periods of time if they are kept moist.
Fasting for 12-24 hours prior to anesthesia is recommended to decrease the incidence of
regurgitation which will foul the water of the anesthetic or recovery container.
Amphibians go through an excitement phase during anesthetic induction. It is important
to induce anesthesia in a container that will prevent injury due to the animal jumping or
falling out.
Pulmonary respiration will cease during anesthesia in amphibians and cannot be used to
monitor anesthetic depth. Cutaneous respiration is sufficient to prevent clinical hypoxia
during anesthesia.
Heart rate may be monitored during anesthesia by direct observation (ventral midline,
caudal to the shoulders). Normal values for heart rates have not been published.
D. Fish anesthesia and analgesia
When a fish reaches the level of anesthesia sufficient to perform surgery, there is a total
loss of equilibrium and muscle tone, decreased respiratory rate and no response to
stimuli. A firm squeeze at the base of the tail may be used to determine response to
stimuli.
Respiratory rate may be evaluated by observing movement of the operculum (rigid flap
that covers the gills) as it opens and closes. Gill color should be dark pink to light red. If
respirations become extremely slow or stop, the fish may be placed in anesthetic-free
recovery water until respirations resume.
Water temperature should be maintained at the species normal optimum during both
anesthesia and recovery.
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